1. Field of the Invention
The present disclosure relates to a method of setting a zero point of a bi-directional linear pump, and more particularly, to a method of setting a zero point of a bi-directional linear pump in an active suspension apparatus for vehicles, which supplies fluid to an actuator assigned to a wheel of a vehicle.
2. Discussion of Related Art
An active suspension system in a vehicle refers to a system which senses various inputs collected from a road through sensors and enables an electric control unit (ECU) to effectively control rolling behavior of the vehicle based on the sensed various inputs.
In particular, the active suspension system may be provided with an actuator compensating a displacement of a coil spring connected to a wheel of a vehicle and may properly control an amount of fluid supplied to the actuator and sense variations of rolling and pitching of the vehicle to constantly maintain a vehicle height above ground, thereby performing a function capable of improving ride comfort of the vehicle and a tire grip force thereof.
In addition, the active suspension system may enable a driver to set a vehicle height above ground according to a road condition through a level control of the vehicle height, or may lower a vehicle height above ground at a high speed to reduce air resistance, thereby performing a function capable of improving a driving stability and fuel efficiency.
In terms of such an active suspension system, U.S. Pat. No. 6,000,702 discloses technical contents in which a spring and a lift-adjustable regulating unit connected thereto in series are included and an amount of fluid supplied to the lift-adjustable regulating unit is adjusted through a proportional control valve.
However, such technical contents have problems in that a high-priced proportional control valve and a high-priced hydraulic pump should be used, and also the hydraulic pump is connected to an engine and is constantly driven due to a structural reason to generate a high pressure source through a constant driving of the hydraulic pump while the engine is running, so that excess capacity not required for the active suspension system is additionally needed and an engine output is reduced, thereby exerting a bad influence to the fuel efficiency.
Moreover, in the patent literature, a bi-directional linear pump may be employed as a pump supplying fluid to such an active suspension system, but a technical feature for locating a piston inside the bi-direction linear pump at a neutral position after supplying the fluid to one side of the active suspension system is not disclosed so that there is a problem in that an effective response against a control input may be very difficult.